Corrosion retarder



Patented Nov. 11, 1952 UNITED STATES greens orrrcs? Hooker Electrochemical Company, Niagara Falls, N. Y., a corporation of New York No Drawing. Original application September 27,

1946, Serial No.

699,640, now Patent No.

2,459,119, dated January 11, 1949. Divided and this application July 30, 1948, Serial No. 41,727

4. Claims.

My invention relates more particularly to retarders of corrosion of metals by acids.

It is known that certain substances exert a protective eifect upon metals, against attack of acids thereon, by rendering the metal passive with respect to the acid, i. e., as anti-catalysts. I will refer to these hereinafter as inhibitors. It is also known that certain other substances exert a protective effect by interposing a film between the metal and the acid. These are of the nature of detergents, or dispersing or Wetting agents, characterized by low surface tension. I will refer to these hereinafter as surface active materials.

Among the agents of the inhibitor category are the aralkyl thio-cyanates, such as benzyl and cymene thio-cyanates. These are typical examples of aralkyl thio-cyanates, each having a methyl group, to which the thio-cyanate group is attached, and the cymene having, in addition, a propyl group. However, these compounds are of low solubility in acid pickling baths. Also, benzyl thio-cyanate has not only an exceedingly disagreeable odor, but toxic and lachrymatory properties, the effects of which are aggravated by its low solubility and consequent tendency to collect at the surface of the bath and spatter into the atmosphere. For these reasons, these compounds have heretofore had little importance, except under conditions permitting of vigorous agitation.

Among the agents of the surface active category are the quaternary ammonium compounds, such as lauryl pyridinium chloride and lauryl dimethyl benzyl ammonium chloride. These are selected examples of quaternary ammonium compounds in which the nitrogen is in the ringand chain respectively. They are not only quite solubl in acid pickling baths, but also have the property of increasing the solubility of other organic compounds, including the thio-cyanates. When used in pickling baths, their saponaceous character causes them to form a foam layer upon the surface.

Th eiiectiveness of these surface active materials is illustrated by the following examples, in which the abbreviations LPG and LDBAC stand for lauryl pyridinium chloride and lauryl dimethyl benzyl ammonium chloride respectively, and the expression protection per cent signifies the extent to which the agent is effective in eliminating corrosion altogether:

Example I Metal, steel Acid, sulphuric, 15% Temperature, C. Corrosion retarder None Percent retarder by weight Weight loss per sq. c. in.

per hour g .119 .048 .0076 Protection, percent 60.0 93.6

It will be seen from the above examples that the addition of minute quantities of these materials to acid pickling baths greatly diminishes the attack upon steel.

I have now found that the analogous quaternary ammonium thio-cyanates, i. e., lauryl pyridinium thio-cyanate and lauryl dimethyl benzyl ammonium thio-cyanate, are very soluble in acid pickling baths, for practical purposes odorless and non-toxic and very efiective as corrosion retarders.

This is illustrated by the following example, to which I have also added benzyl pyridinium thicyanate for comparison, and in which these compounds are denoted by the abbreviations LDBATC, LPTC and BPTC respectively:

Example II LPC LDBAC Metal, steel Acid, sulphuric, 15% Temperature, 75 C. Corrosion retarder None LDBATC ercent retarder by weight Weight loss per sq.

c. m. per hr. g .119 .0047 .0021 Protection, percent 96.0 98.2

It will be seen by comparison Examples I and II that these alkyl quaternary ammonium thiocyanates are much more effective as retarders of corros1on than the corresponding chlorides. It W111 also be seen that these alkyl quaternary am- LPTC BPTC

monium thio-cyanates are much superior to the Protection, Wt. Percent Percent Triethylamine 0. 15 10. Aniline 0. 09 14. 5 Pyridine 0. 08 19.0 Quinoline- 0. 13 49. 4 Acridine. 0. 18 82. 4 2-me-quinol1ne 0. 53. 0 me-acridine 0. 20 81.8 Phenyl acridine 0. 29 90. 2 Nitrogen bases 0.1 88. Lauryl pyridinium chloride 0. 1 85. Lauryl dimcthyl benzyl ammo um thio-cyanate 1 0. 02 96, Lauryl pyridinium thio-cyanate 0.02 98. 2 Lauryl pyridinium thio-cyanate 0.01 90. 4

t will be seen from the above that lauryl dimethyl benzyl ammonium thio-cyanate and lauryl pyridinium thio-cyanate rank high among corrosion retarders, and when it is remembered that they, have the advantage over most of them of high water solubility, non-toxicity, and freedom from offensive odor, theirimportance as corrosion retarders will be manifest.

Corrosion retarders are useful Wherever acids are handled in metal equipment, of which pickling of metal is only one of many illustrations, acid treatment of oil wells being another. Another use of such retarders is in lubricants, which are liable to develop acidity through oxidation, by contact with air. Organic acids developed in lubricating oils, such as those used in automotive crankcases, are mild compared with pickling acids, but the time factor is measured in months, instead of hours, and in the long run the corrosive effect of such acids may be very serious, especially upon bearing alloys such as those composed of lead, tin, copper and less common metals. It is difficult to give a quantitative measure of the effect of corrosion retarders in lubricating oils, as the matter is complicated by wear. Nevertheless,

visual comparison of the effects of lubricating oils upon bearings, with and without my retarders, indicates that my retarders have a useful effect in such oils.

While I have given examples of the results obtained with my compositions only in proportions ranging from 0.02 to 0.1 per cent by weight, I do not wish to be held to these limits, as my retarders are useful in proportions as low as .005 per cent, and there is no objection to using up to 5 per cent of the retarder.

This application is a division of my co-pending application, Serial Number 699,640 filed September 27, 1946, now Patent No. 2,459,119 issued January 11, 1949.

I claim as my invention:

1. A composition substantially non-corrosive to metals comprising a dilute aqeous solution of an inorganic acid and 0.005 to 5 per cent by weight of a quaternary ammonium compound selected from the group consisting of lauryl pyridinium thiocyanate and lauryl dimethyl benzyl ammonium thiocyanate.

2. A composition substantially non-corrosive to metals comprising a dilute aqueous solution of sulfuric acid and 0.005 to 5 per cent by weight of lauryl pyridinium thiocyanate.

3. A composition substantially non-corrosive to metals comprising a dilute aqueous solution of sulfuric acid and 0.005 to 5' percent by weight of lauryl dimethyl benzyl amino'ni'num thiocyanate.

4. The method of protecting metals against corrosion by dilute aqueous acids which comprises incorporating in the acid 0.005 to 5.0 per cent by weight of a quaternary ammonium compound selected from the group consisting of lauryl pyridinium thiocyanate and lauryl dimethyl benzyl ammonium thiocyanate.

JOHN T. RUCKER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,006,216 MacArthur et a1. June 25, 1 935 2,203,649 Felkers June 4, 1940 2,254,940 Endres Sept. 2, 1941 2,321,517 Rosen June 8, 1943 2,340,996 Smyers Feb. 8, 1944 2,402,526 Pikl -1 June 18, 1946 

4. THE METHOD OF PROTECTING METALS AGAINST CORROSION BY DILUTE AQUEOUS ACIDS WHICH COMPRISES INCORPORATING IN THE ACID 0.005 TO 5.0 PER CENT BY WEIGHT OF A QUATERNARY AMMONIUM COMPOUND SELECTED FROM THE GROUP CONSISTING OF LAURYL PYRIDINIUM THIOCYANATE AND LAURYL DIMETHYL BENZYL AMMONIUM THIOCYANATE. 